Commit | Line | Data |
---|---|---|
7f918cf1 CE |
1 | <!DOCTYPE html>\r |
2 | <html lang="en">\r | |
3 | <head>\r | |
4 | <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">\r | |
5 | <meta name="generator" content="AsciiDoc 8.6.9">\r | |
6 | <title>SMLNJDeviations</title>\r | |
7 | <link rel="stylesheet" href="./asciidoc.css" type="text/css">\r | |
8 | <link rel="stylesheet" href="./pygments.css" type="text/css">\r | |
9 | \r | |
10 | \r | |
11 | <script type="text/javascript" src="./asciidoc.js"></script>\r | |
12 | <script type="text/javascript">\r | |
13 | /*<![CDATA[*/\r | |
14 | asciidoc.install();\r | |
15 | /*]]>*/\r | |
16 | </script>\r | |
17 | <link rel="stylesheet" href="./mlton.css" type="text/css">\r | |
18 | </head>\r | |
19 | <body class="article">\r | |
20 | <div id="banner">\r | |
21 | <div id="banner-home">\r | |
22 | <a href="./Home">MLton 20180207</a>\r | |
23 | </div>\r | |
24 | </div>\r | |
25 | <div id="header">\r | |
26 | <h1>SMLNJDeviations</h1>\r | |
27 | </div>\r | |
28 | <div id="content">\r | |
29 | <div id="preamble">\r | |
30 | <div class="sectionbody">\r | |
31 | <div class="paragraph"><p>Here are some deviations of <a href="SMLNJ">SML/NJ</a> from\r | |
32 | <a href="DefinitionOfStandardML">The Definition of Standard ML (Revised)</a>.\r | |
33 | Some of these are documented in the\r | |
34 | <a href="http://www.smlnj.org/doc/Conversion/index.html">SML '97 Conversion Guide</a>.\r | |
35 | Since MLton does not deviate from the Definition, you should look here\r | |
36 | if you are having trouble porting a program from MLton to SML/NJ or\r | |
37 | vice versa. If you discover other deviations of SML/NJ that aren’t\r | |
38 | listed here, please send mail to\r | |
39 | <a href="mailto:MLton-devel@mlton.org"><span class="monospaced">MLton-devel@mlton.org</span></a>.</p></div>\r | |
40 | <div class="ulist"><ul>\r | |
41 | <li>\r | |
42 | <p>\r | |
43 | SML/NJ allows spaces in long identifiers, as in <span class="monospaced">S . x</span>. Section\r | |
44 | 2.5 of the Definition implies that <span class="monospaced">S . x</span> should be treated as three\r | |
45 | separate lexical items.\r | |
46 | </p>\r | |
47 | </li>\r | |
48 | <li>\r | |
49 | <p>\r | |
50 | SML/NJ allows <span class="monospaced">op</span> to appear in <span class="monospaced">val</span> specifications:\r | |
51 | </p>\r | |
52 | <div class="listingblock">\r | |
53 | <div class="content"><div class="highlight"><pre><span class="k">signature</span><span class="w"> </span><span class="n">FOO</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="k">sig</span><span class="w"></span>\r | |
54 | <span class="w"> </span><span class="k">val</span><span class="w"> </span><span class="k">op</span><span class="w"> </span><span class="n">+</span><span class="w"> </span><span class="p">:</span><span class="w"> </span><span class="n">int</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">int</span><span class="w"> </span><span class="p">-></span><span class="w"> </span><span class="n">int</span><span class="w"></span>\r | |
55 | <span class="k">end</span><span class="w"></span>\r | |
56 | </pre></div></div></div>\r | |
57 | <div class="paragraph"><p>The grammar on page 14 of the Definition does not allow it. Recent\r | |
58 | versions of SML/NJ do give a warning.</p></div>\r | |
59 | </li>\r | |
60 | <li>\r | |
61 | <p>\r | |
62 | SML/NJ rejects\r | |
63 | </p>\r | |
64 | <div class="listingblock">\r | |
65 | <div class="content"><div class="highlight"><pre><span class="p">(</span><span class="k">op</span><span class="w"> </span><span class="n">*</span><span class="p">)</span><span class="w"></span>\r | |
66 | </pre></div></div></div>\r | |
67 | <div class="paragraph"><p>as an unmatched close comment.</p></div>\r | |
68 | </li>\r | |
69 | <li>\r | |
70 | <p>\r | |
71 | SML/NJ allows <span class="monospaced">=</span> to be rebound by the declaration:\r | |
72 | </p>\r | |
73 | <div class="listingblock">\r | |
74 | <div class="content"><div class="highlight"><pre><span class="k">val</span><span class="w"> </span><span class="k">op</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="mi">13</span><span class="w"></span>\r | |
75 | </pre></div></div></div>\r | |
76 | <div class="paragraph"><p>This is explicitly forbidden on page 5 of the Definition. Recent\r | |
77 | versions of SML/NJ do give a warning.</p></div>\r | |
78 | </li>\r | |
79 | <li>\r | |
80 | <p>\r | |
81 | SML/NJ allows rebinding <span class="monospaced">true</span>, <span class="monospaced">false</span>, <span class="monospaced">nil</span>, <span class="monospaced">::</span>, and <span class="monospaced">ref</span> by\r | |
82 | the declarations:\r | |
83 | </p>\r | |
84 | <div class="listingblock">\r | |
85 | <div class="content"><div class="highlight"><pre><span class="k">fun</span><span class="w"> </span><span class="n">true</span><span class="w"> </span><span class="p">()</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="p">()</span><span class="w"></span>\r | |
86 | <span class="k">fun</span><span class="w"> </span><span class="n">false</span><span class="w"> </span><span class="p">()</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="p">()</span><span class="w"></span>\r | |
87 | <span class="k">fun</span><span class="w"> </span><span class="n">nil</span><span class="w"> </span><span class="p">()</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="p">()</span><span class="w"></span>\r | |
88 | <span class="k">fun</span><span class="w"> </span><span class="k">op</span><span class="w"> </span><span class="n">::</span><span class="w"> </span><span class="p">()</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="p">()</span><span class="w"></span>\r | |
89 | <span class="k">fun</span><span class="w"> </span><span class="n">ref</span><span class="w"> </span><span class="p">()</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="p">()</span><span class="w"></span>\r | |
90 | </pre></div></div></div>\r | |
91 | <div class="paragraph"><p>This is explicitly forbidden on page 9 of the Definition.</p></div>\r | |
92 | </li>\r | |
93 | <li>\r | |
94 | <p>\r | |
95 | SML/NJ extends the syntax of the language to allow vector\r | |
96 | expressions and patterns like the following:\r | |
97 | </p>\r | |
98 | <div class="listingblock">\r | |
99 | <div class="content"><div class="highlight"><pre><span class="k">val</span><span class="w"> </span><span class="n">v</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="p">#[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">]</span><span class="w"></span>\r | |
100 | <span class="k">val</span><span class="w"> </span><span class="p">#[</span><span class="n">x</span><span class="p">,</span><span class="n">y</span><span class="p">,</span><span class="n">z</span><span class="p">]</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">v</span><span class="w"></span>\r | |
101 | </pre></div></div></div>\r | |
102 | <div class="paragraph"><p>MLton supports vector expressions and patterns with the <a href="SuccessorML#VectorExpsAndPats"><span class="monospaced">allowVectorExpsAndPats</span></a> <a href="MLBasisAnnotations">ML Basis annotation</a>.</p></div>\r | |
103 | </li>\r | |
104 | <li>\r | |
105 | <p>\r | |
106 | SML/NJ extends the syntax of the language to allow <em>or patterns</em>\r | |
107 | like the following:\r | |
108 | </p>\r | |
109 | <div class="listingblock">\r | |
110 | <div class="content"><div class="highlight"><pre><span class="k">datatype</span><span class="w"> </span><span class="n">foo</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">Foo</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="n">int</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Bar</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="n">int</span><span class="w"></span>\r | |
111 | <span class="k">val</span><span class="w"> </span><span class="p">(</span><span class="n">Foo</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">Bar</span><span class="w"> </span><span class="n">x</span><span class="p">)</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">Foo</span><span class="w"> </span><span class="mi">13</span><span class="w"></span>\r | |
112 | </pre></div></div></div>\r | |
113 | <div class="paragraph"><p>MLton supports or patterns with the <a href="SuccessorML#OrPats"><span class="monospaced">allowOrPats</span></a> <a href="MLBasisAnnotations">ML Basis annotation</a>.</p></div>\r | |
114 | </li>\r | |
115 | <li>\r | |
116 | <p>\r | |
117 | SML/NJ allows higher-order functors, that is, functors can be\r | |
118 | components of structures and can be passed as functor arguments and\r | |
119 | returned as functor results. As a consequence, SML/NJ allows\r | |
120 | abbreviated functor definitions, as in the following:\r | |
121 | </p>\r | |
122 | <div class="listingblock">\r | |
123 | <div class="content"><div class="highlight"><pre><span class="k">signature</span><span class="w"> </span><span class="n">S</span><span class="w"> </span><span class="p">=</span><span class="w"></span>\r | |
124 | <span class="w"> </span><span class="k">sig</span><span class="w"></span>\r | |
125 | <span class="w"> </span><span class="k">type</span><span class="w"> </span><span class="n">t</span><span class="w"></span>\r | |
126 | <span class="w"> </span><span class="k">val</span><span class="w"> </span><span class="n">x</span><span class="p">:</span><span class="w"> </span><span class="n">t</span><span class="w"></span>\r | |
127 | <span class="w"> </span><span class="k">end</span><span class="w"></span>\r | |
128 | <span class="k">functor</span><span class="w"> </span><span class="n">F</span><span class="w"> </span><span class="p">(</span><span class="k">structure</span><span class="w"> </span><span class="n">A</span><span class="p">:</span><span class="w"> </span><span class="n">S</span><span class="p">):</span><span class="w"> </span><span class="n">S</span><span class="w"> </span><span class="p">=</span><span class="w"></span>\r | |
129 | <span class="w"> </span><span class="k">struct</span><span class="w"></span>\r | |
130 | <span class="w"> </span><span class="k">type</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">A</span><span class="p">.</span><span class="n">t</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">A</span><span class="p">.</span><span class="n">t</span><span class="w"></span>\r | |
131 | <span class="w"> </span><span class="k">val</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="p">(</span><span class="n">A</span><span class="p">.</span><span class="n">x</span><span class="p">,</span><span class="w"> </span><span class="n">A</span><span class="p">.</span><span class="n">x</span><span class="p">)</span><span class="w"></span>\r | |
132 | <span class="w"> </span><span class="k">end</span><span class="w"></span>\r | |
133 | <span class="k">functor</span><span class="w"> </span><span class="n">G</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">F</span><span class="w"></span>\r | |
134 | </pre></div></div></div>\r | |
135 | </li>\r | |
136 | <li>\r | |
137 | <p>\r | |
138 | SML/NJ extends the syntax of the language to allow <span class="monospaced">functor</span> and\r | |
139 | <span class="monospaced">signature</span> declarations to occur within the scope of <span class="monospaced">local</span> and\r | |
140 | <span class="monospaced">structure</span> declarations.\r | |
141 | </p>\r | |
142 | </li>\r | |
143 | <li>\r | |
144 | <p>\r | |
145 | SML/NJ allows duplicate type specifications in signatures when the\r | |
146 | duplicates are introduced by <span class="monospaced">include</span>, as in the following:\r | |
147 | </p>\r | |
148 | <div class="listingblock">\r | |
149 | <div class="content"><div class="highlight"><pre><span class="k">signature</span><span class="w"> </span><span class="n">SIG1</span><span class="w"> </span><span class="p">=</span><span class="w"></span>\r | |
150 | <span class="w"> </span><span class="k">sig</span><span class="w"></span>\r | |
151 | <span class="w"> </span><span class="k">type</span><span class="w"> </span><span class="n">t</span><span class="w"></span>\r | |
152 | <span class="w"> </span><span class="k">type</span><span class="w"> </span><span class="n">u</span><span class="w"></span>\r | |
153 | <span class="w"> </span><span class="k">end</span><span class="w"></span>\r | |
154 | <span class="k">signature</span><span class="w"> </span><span class="n">SIG2</span><span class="w"> </span><span class="p">=</span><span class="w"></span>\r | |
155 | <span class="w"> </span><span class="k">sig</span><span class="w"></span>\r | |
156 | <span class="w"> </span><span class="k">type</span><span class="w"> </span><span class="n">t</span><span class="w"></span>\r | |
157 | <span class="w"> </span><span class="k">type</span><span class="w"> </span><span class="n">v</span><span class="w"></span>\r | |
158 | <span class="w"> </span><span class="k">end</span><span class="w"></span>\r | |
159 | <span class="k">signature</span><span class="w"> </span><span class="n">SIG</span><span class="w"> </span><span class="p">=</span><span class="w"></span>\r | |
160 | <span class="w"> </span><span class="k">sig</span><span class="w"></span>\r | |
161 | <span class="w"> </span><span class="k">include</span><span class="w"> </span><span class="n">SIG1</span><span class="w"></span>\r | |
162 | <span class="w"> </span><span class="k">include</span><span class="w"> </span><span class="n">SIG2</span><span class="w"></span>\r | |
163 | <span class="w"> </span><span class="k">end</span><span class="w"></span>\r | |
164 | </pre></div></div></div>\r | |
165 | <div class="paragraph"><p>This is disallowed by rule 77 of the Definition.</p></div>\r | |
166 | </li>\r | |
167 | <li>\r | |
168 | <p>\r | |
169 | SML/NJ allows sharing constraints between type abbreviations in\r | |
170 | signatures, as in the following:\r | |
171 | </p>\r | |
172 | <div class="listingblock">\r | |
173 | <div class="content"><div class="highlight"><pre><span class="k">signature</span><span class="w"> </span><span class="n">SIG</span><span class="w"> </span><span class="p">=</span><span class="w"></span>\r | |
174 | <span class="w"> </span><span class="k">sig</span><span class="w"></span>\r | |
175 | <span class="w"> </span><span class="k">type</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">int</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">int</span><span class="w"></span>\r | |
176 | <span class="w"> </span><span class="k">type</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">int</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">int</span><span class="w"></span>\r | |
177 | <span class="w"> </span><span class="k">sharing</span><span class="w"> </span><span class="k">type</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">u</span><span class="w"></span>\r | |
178 | <span class="w"> </span><span class="k">end</span><span class="w"></span>\r | |
179 | </pre></div></div></div>\r | |
180 | <div class="paragraph"><p>These are disallowed by rule 78 of the Definition. Recent versions of\r | |
181 | SML/NJ correctly disallow sharing constraints between type\r | |
182 | abbreviations in signatures.</p></div>\r | |
183 | </li>\r | |
184 | <li>\r | |
185 | <p>\r | |
186 | SML/NJ disallows multiple <span class="monospaced">where type</span> specifications of the same\r | |
187 | type name, as in the following\r | |
188 | </p>\r | |
189 | <div class="listingblock">\r | |
190 | <div class="content"><div class="highlight"><pre><span class="k">signature</span><span class="w"> </span><span class="n">S</span><span class="w"> </span><span class="p">=</span><span class="w"></span>\r | |
191 | <span class="w"> </span><span class="k">sig</span><span class="w"></span>\r | |
192 | <span class="w"> </span><span class="k">type</span><span class="w"> </span><span class="n">t</span><span class="w"></span>\r | |
193 | <span class="w"> </span><span class="k">type</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">t</span><span class="w"></span>\r | |
194 | <span class="w"> </span><span class="k">end</span><span class="w"></span>\r | |
195 | <span class="w"> </span><span class="k">where</span><span class="w"> </span><span class="k">type</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">int</span><span class="w"></span>\r | |
196 | </pre></div></div></div>\r | |
197 | <div class="paragraph"><p>This is allowed by rule 64 of the Definition.</p></div>\r | |
198 | </li>\r | |
199 | <li>\r | |
200 | <p>\r | |
201 | SML/NJ allows <span class="monospaced">and</span> in <span class="monospaced">sharing</span> specs in signatures, as in\r | |
202 | </p>\r | |
203 | <div class="listingblock">\r | |
204 | <div class="content"><div class="highlight"><pre><span class="k">signature</span><span class="w"> </span><span class="n">S</span><span class="w"> </span><span class="p">=</span><span class="w"></span>\r | |
205 | <span class="w"> </span><span class="k">sig</span><span class="w"></span>\r | |
206 | <span class="w"> </span><span class="k">type</span><span class="w"> </span><span class="n">t</span><span class="w"></span>\r | |
207 | <span class="w"> </span><span class="k">type</span><span class="w"> </span><span class="n">u</span><span class="w"></span>\r | |
208 | <span class="w"> </span><span class="k">type</span><span class="w"> </span><span class="n">v</span><span class="w"></span>\r | |
209 | <span class="w"> </span><span class="k">sharing</span><span class="w"> </span><span class="k">type</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">u</span><span class="w"></span>\r | |
210 | <span class="w"> </span><span class="k">and</span><span class="w"> </span><span class="k">type</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">v</span><span class="w"></span>\r | |
211 | <span class="w"> </span><span class="k">end</span><span class="w"></span>\r | |
212 | </pre></div></div></div>\r | |
213 | </li>\r | |
214 | <li>\r | |
215 | <p>\r | |
216 | SML/NJ does not expand the <span class="monospaced">withtype</span> derived form as described by\r | |
217 | the Definition. According to page 55 of the Definition, the type\r | |
218 | bindings of a <span class="monospaced">withtype</span> declaration are substituted simultaneously in\r | |
219 | the connected datatype. Consider the following program.\r | |
220 | </p>\r | |
221 | <div class="listingblock">\r | |
222 | <div class="content"><div class="highlight"><pre><span class="k">type</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">real</span><span class="w"> </span><span class="p">;</span><span class="w"></span>\r | |
223 | <span class="k">datatype</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="p">=</span><span class="w"></span>\r | |
224 | <span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="n">t</span><span class="w"></span>\r | |
225 | <span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="n">u</span><span class="w"></span>\r | |
226 | <span class="k">withtype</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">int</span><span class="w"></span>\r | |
227 | <span class="k">and</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">u</span><span class="w"></span>\r | |
228 | </pre></div></div></div>\r | |
229 | <div class="paragraph"><p>According to the Definition, it should be expanded to the following.</p></div>\r | |
230 | <div class="listingblock">\r | |
231 | <div class="content"><div class="highlight"><pre><span class="k">type</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">real</span><span class="w"> </span><span class="p">;</span><span class="w"></span>\r | |
232 | <span class="k">datatype</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="p">=</span><span class="w"></span>\r | |
233 | <span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="n">u</span><span class="w"></span>\r | |
234 | <span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="n">int</span><span class="w"> </span><span class="p">;</span><span class="w"></span>\r | |
235 | <span class="k">type</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">int</span><span class="w"></span>\r | |
236 | <span class="k">and</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">u</span><span class="w"></span>\r | |
237 | </pre></div></div></div>\r | |
238 | <div class="paragraph"><p>However, SML/NJ expands <span class="monospaced">withtype</span> bindings sequentially, meaning that\r | |
239 | earlier bindings are expanded within later ones. Hence, the above\r | |
240 | program is expanded to the following.</p></div>\r | |
241 | <div class="listingblock">\r | |
242 | <div class="content"><div class="highlight"><pre><span class="k">type</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">real</span><span class="w"> </span><span class="p">;</span><span class="w"></span>\r | |
243 | <span class="k">datatype</span><span class="w"> </span><span class="n">a</span><span class="w"> </span><span class="p">=</span><span class="w"></span>\r | |
244 | <span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="n">int</span><span class="w"></span>\r | |
245 | <span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="n">int</span><span class="w"> </span><span class="p">;</span><span class="w"></span>\r | |
246 | <span class="k">type</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">int</span><span class="w"></span>\r | |
247 | <span class="k">type</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">int</span><span class="w"></span>\r | |
248 | </pre></div></div></div>\r | |
249 | </li>\r | |
250 | <li>\r | |
251 | <p>\r | |
252 | SML/NJ allows <span class="monospaced">withtype</span> specifications in signatures.\r | |
253 | </p>\r | |
254 | <div class="paragraph"><p>MLton supports <span class="monospaced">withtype</span> specifications in signatures with the <a href="SuccessorML#SigWithtype"><span class="monospaced">allowSigWithtype</span></a> <a href="MLBasisAnnotations">ML Basis annotation</a>.</p></div>\r | |
255 | </li>\r | |
256 | <li>\r | |
257 | <p>\r | |
258 | SML/NJ allows a <span class="monospaced">where</span> structure specification that is similar to a\r | |
259 | <span class="monospaced">where type</span> specification. For example:\r | |
260 | </p>\r | |
261 | <div class="listingblock">\r | |
262 | <div class="content"><div class="highlight"><pre><span class="k">structure</span><span class="w"> </span><span class="n">S</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="k">type</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">int</span><span class="w"> </span><span class="k">end</span><span class="w"></span>\r | |
263 | <span class="k">signature</span><span class="w"> </span><span class="n">SIG</span><span class="w"> </span><span class="p">=</span><span class="w"></span>\r | |
264 | <span class="w"> </span><span class="k">sig</span><span class="w"></span>\r | |
265 | <span class="w"> </span><span class="k">structure</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="p">:</span><span class="w"> </span><span class="k">sig</span><span class="w"> </span><span class="k">type</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="k">end</span><span class="w"></span>\r | |
266 | <span class="w"> </span><span class="k">end</span><span class="w"> </span><span class="k">where</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">S</span><span class="w"></span>\r | |
267 | </pre></div></div></div>\r | |
268 | <div class="paragraph"><p>This is equivalent to:</p></div>\r | |
269 | <div class="listingblock">\r | |
270 | <div class="content"><div class="highlight"><pre><span class="k">structure</span><span class="w"> </span><span class="n">S</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="k">type</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">int</span><span class="w"> </span><span class="k">end</span><span class="w"></span>\r | |
271 | <span class="k">signature</span><span class="w"> </span><span class="n">SIG</span><span class="w"> </span><span class="p">=</span><span class="w"></span>\r | |
272 | <span class="w"> </span><span class="k">sig</span><span class="w"></span>\r | |
273 | <span class="w"> </span><span class="k">structure</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="p">:</span><span class="w"> </span><span class="k">sig</span><span class="w"> </span><span class="k">type</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="k">end</span><span class="w"></span>\r | |
274 | <span class="w"> </span><span class="k">end</span><span class="w"> </span><span class="k">where</span><span class="w"> </span><span class="k">type</span><span class="w"> </span><span class="n">T</span><span class="p">.</span><span class="n">t</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">S</span><span class="p">.</span><span class="n">t</span><span class="w"></span>\r | |
275 | </pre></div></div></div>\r | |
276 | <div class="paragraph"><p>SML/NJ also allows a definitional structure specification that is\r | |
277 | similar to a definitional type specification. For example:</p></div>\r | |
278 | <div class="listingblock">\r | |
279 | <div class="content"><div class="highlight"><pre><span class="k">structure</span><span class="w"> </span><span class="n">S</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="k">type</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">int</span><span class="w"> </span><span class="k">end</span><span class="w"></span>\r | |
280 | <span class="k">signature</span><span class="w"> </span><span class="n">SIG</span><span class="w"> </span><span class="p">=</span><span class="w"></span>\r | |
281 | <span class="w"> </span><span class="k">sig</span><span class="w"></span>\r | |
282 | <span class="w"> </span><span class="k">structure</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="p">:</span><span class="w"> </span><span class="k">sig</span><span class="w"> </span><span class="k">type</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="k">end</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">S</span><span class="w"></span>\r | |
283 | <span class="w"> </span><span class="k">end</span><span class="w"></span>\r | |
284 | </pre></div></div></div>\r | |
285 | <div class="paragraph"><p>This is equivalent to the previous examples and to:</p></div>\r | |
286 | <div class="listingblock">\r | |
287 | <div class="content"><div class="highlight"><pre><span class="k">structure</span><span class="w"> </span><span class="n">S</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="k">struct</span><span class="w"> </span><span class="k">type</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">int</span><span class="w"> </span><span class="k">end</span><span class="w"></span>\r | |
288 | <span class="k">signature</span><span class="w"> </span><span class="n">SIG</span><span class="w"> </span><span class="p">=</span><span class="w"></span>\r | |
289 | <span class="w"> </span><span class="k">sig</span><span class="w"></span>\r | |
290 | <span class="w"> </span><span class="k">structure</span><span class="w"> </span><span class="n">T</span><span class="w"> </span><span class="p">:</span><span class="w"> </span><span class="k">sig</span><span class="w"> </span><span class="k">type</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="k">end</span><span class="w"> </span><span class="k">where</span><span class="w"> </span><span class="k">type</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">S</span><span class="p">.</span><span class="n">t</span><span class="w"></span>\r | |
291 | <span class="w"> </span><span class="k">end</span><span class="w"></span>\r | |
292 | </pre></div></div></div>\r | |
293 | </li>\r | |
294 | <li>\r | |
295 | <p>\r | |
296 | SML/NJ disallows binding non-datatypes with datatype replication.\r | |
297 | For example, it rejects the following program that should be allowed\r | |
298 | according to the Definition.\r | |
299 | </p>\r | |
300 | <div class="listingblock">\r | |
301 | <div class="content"><div class="highlight"><pre><span class="k">type</span><span class="w"> </span><span class="p">(</span><span class="n">'a</span><span class="p">,</span><span class="w"> </span><span class="n">'b</span><span class="p">)</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">'a</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">'b</span><span class="w"></span>\r | |
302 | <span class="k">datatype</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="k">datatype</span><span class="w"> </span><span class="n">t</span><span class="w"></span>\r | |
303 | </pre></div></div></div>\r | |
304 | <div class="paragraph"><p>This idiom can be useful when one wants to rename a type without\r | |
305 | rewriting all the type arguments. For example, the above would have\r | |
306 | to be written in SML/NJ as follows.</p></div>\r | |
307 | <div class="listingblock">\r | |
308 | <div class="content"><div class="highlight"><pre><span class="k">type</span><span class="w"> </span><span class="p">(</span><span class="n">'a</span><span class="p">,</span><span class="w"> </span><span class="n">'b</span><span class="p">)</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">'a</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">'b</span><span class="w"></span>\r | |
309 | <span class="k">type</span><span class="w"> </span><span class="p">(</span><span class="n">'a</span><span class="p">,</span><span class="w"> </span><span class="n">'b</span><span class="p">)</span><span class="w"> </span><span class="n">u</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="p">(</span><span class="n">'a</span><span class="p">,</span><span class="w"> </span><span class="n">'b</span><span class="p">)</span><span class="w"> </span><span class="n">t</span><span class="w"></span>\r | |
310 | </pre></div></div></div>\r | |
311 | </li>\r | |
312 | <li>\r | |
313 | <p>\r | |
314 | SML/NJ disallows sharing a structure with one of its substructures.\r | |
315 | For example, SML/NJ disallows the following.\r | |
316 | </p>\r | |
317 | <div class="listingblock">\r | |
318 | <div class="content"><div class="highlight"><pre><span class="k">signature</span><span class="w"> </span><span class="n">SIG</span><span class="w"> </span><span class="p">=</span><span class="w"></span>\r | |
319 | <span class="w"> </span><span class="k">sig</span><span class="w"></span>\r | |
320 | <span class="w"> </span><span class="k">structure</span><span class="w"> </span><span class="n">S</span><span class="p">:</span><span class="w"></span>\r | |
321 | <span class="w"> </span><span class="k">sig</span><span class="w"></span>\r | |
322 | <span class="w"> </span><span class="k">type</span><span class="w"> </span><span class="n">t</span><span class="w"></span>\r | |
323 | <span class="w"> </span><span class="k">structure</span><span class="w"> </span><span class="n">T</span><span class="p">:</span><span class="w"> </span><span class="k">sig</span><span class="w"> </span><span class="k">type</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="k">end</span><span class="w"></span>\r | |
324 | <span class="w"> </span><span class="k">end</span><span class="w"></span>\r | |
325 | <span class="w"> </span><span class="k">sharing</span><span class="w"> </span><span class="n">S</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">S</span><span class="p">.</span><span class="n">T</span><span class="w"></span>\r | |
326 | <span class="w"> </span><span class="k">end</span><span class="w"></span>\r | |
327 | </pre></div></div></div>\r | |
328 | <div class="paragraph"><p>This signature is allowed by the Definition.</p></div>\r | |
329 | </li>\r | |
330 | <li>\r | |
331 | <p>\r | |
332 | SML/NJ disallows polymorphic generalization of refutable\r | |
333 | patterns. For example, SML/NJ disallows the following.\r | |
334 | </p>\r | |
335 | <div class="listingblock">\r | |
336 | <div class="content"><div class="highlight"><pre><span class="k">val</span><span class="w"> </span><span class="p">[</span><span class="n">x</span><span class="p">]</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="p">[[]]</span><span class="w"></span>\r | |
337 | <span class="k">val</span><span class="w"> </span><span class="p">_</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="p">(</span><span class="mi">1</span><span class="w"> </span><span class="n">::</span><span class="w"> </span><span class="n">x</span><span class="p">,</span><span class="w"> </span><span class="s">"one"</span><span class="w"> </span><span class="n">::</span><span class="w"> </span><span class="n">x</span><span class="p">)</span><span class="w"></span>\r | |
338 | </pre></div></div></div>\r | |
339 | <div class="paragraph"><p>Recent versions of SML/NJ correctly allow polymorphic generalization\r | |
340 | of refutable patterns.</p></div>\r | |
341 | </li>\r | |
342 | <li>\r | |
343 | <p>\r | |
344 | SML/NJ uses an overly restrictive context for type inference. For\r | |
345 | example, SML/NJ rejects both of the following.\r | |
346 | </p>\r | |
347 | <div class="listingblock">\r | |
348 | <div class="content"><div class="highlight"><pre><span class="k">structure</span><span class="w"> </span><span class="n">S</span><span class="w"> </span><span class="p">=</span><span class="w"></span>\r | |
349 | <span class="k">struct</span><span class="w"></span>\r | |
350 | <span class="w"> </span><span class="k">val</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="p">(</span><span class="k">fn</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="p">=></span><span class="w"> </span><span class="n">x</span><span class="p">)</span><span class="w"> </span><span class="p">[]</span><span class="w"></span>\r | |
351 | <span class="w"> </span><span class="k">val</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="n">::</span><span class="w"> </span><span class="p">[</span><span class="n">true</span><span class="p">]</span><span class="w"> </span><span class="n">::</span><span class="w"> </span><span class="n">nil</span><span class="w"></span>\r | |
352 | <span class="k">end</span><span class="w"></span>\r | |
353 | </pre></div></div></div>\r | |
354 | <div class="listingblock">\r | |
355 | <div class="content"><div class="highlight"><pre><span class="k">structure</span><span class="w"> </span><span class="n">S</span><span class="w"> </span><span class="p">:</span><span class="w"> </span><span class="k">sig</span><span class="w"> </span><span class="k">val</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="p">:</span><span class="w"> </span><span class="n">bool</span><span class="w"> </span><span class="n">list</span><span class="w"> </span><span class="k">end</span><span class="w"> </span><span class="p">=</span><span class="w"></span>\r | |
356 | <span class="k">struct</span><span class="w"></span>\r | |
357 | <span class="w"> </span><span class="k">val</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="p">(</span><span class="k">fn</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="p">=></span><span class="w"> </span><span class="n">x</span><span class="p">)</span><span class="w"> </span><span class="p">[]</span><span class="w"></span>\r | |
358 | <span class="k">end</span><span class="w"></span>\r | |
359 | </pre></div></div></div>\r | |
360 | <div class="paragraph"><p>These structures are allowed by the Definition.</p></div>\r | |
361 | </li>\r | |
362 | </ul></div>\r | |
363 | </div>\r | |
364 | </div>\r | |
365 | <div class="sect1">\r | |
366 | <h2 id="_deviations_from_the_basis_library_specification">Deviations from the Basis Library Specification</h2>\r | |
367 | <div class="sectionbody">\r | |
368 | <div class="paragraph"><p>Here are some deviations of SML/NJ from the <a href="BasisLibrary">Basis Library</a>\r | |
369 | <a href="http://www.standardml.org/Basis">specification</a>.</p></div>\r | |
370 | <div class="ulist"><ul>\r | |
371 | <li>\r | |
372 | <p>\r | |
373 | SML/NJ exposes the equality of the <span class="monospaced">vector</span> type in structures such\r | |
374 | as <span class="monospaced">Word8Vector</span> that abstractly match <span class="monospaced">MONO_VECTOR</span>, which says\r | |
375 | <span class="monospaced">type vector</span>, not <span class="monospaced">eqtype vector</span>. So, for example, SML/NJ accepts\r | |
376 | the following program:\r | |
377 | </p>\r | |
378 | <div class="listingblock">\r | |
379 | <div class="content"><div class="highlight"><pre><span class="k">fun</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="p">(</span><span class="n">v</span><span class="p">:</span><span class="w"> </span><span class="n">Word8Vector</span><span class="p">.</span><span class="n">vector</span><span class="p">)</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">v</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">v</span><span class="w"></span>\r | |
380 | </pre></div></div></div>\r | |
381 | </li>\r | |
382 | <li>\r | |
383 | <p>\r | |
384 | SML/NJ exposes the equality property of the type <span class="monospaced">status</span> in\r | |
385 | <span class="monospaced">OS.Process</span>. This means that programs which directly compare two\r | |
386 | values of type <span class="monospaced">status</span> will work with SML/NJ but not MLton.\r | |
387 | </p>\r | |
388 | </li>\r | |
389 | <li>\r | |
390 | <p>\r | |
391 | Under SML/NJ on Windows, <span class="monospaced">OS.Path.validVolume</span> incorrectly considers\r | |
392 | absolute empty volumes to be valid. In other words, when the\r | |
393 | expression\r | |
394 | </p>\r | |
395 | <div class="listingblock">\r | |
396 | <div class="content"><div class="highlight"><pre><span class="n">OS</span><span class="p">.</span><span class="n">Path</span><span class="p">.</span><span class="n">validVolume</span><span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="n">isAbs</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">true</span><span class="p">,</span><span class="w"> </span><span class="n">vol</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="s">""</span><span class="w"> </span><span class="p">}</span><span class="w"></span>\r | |
397 | </pre></div></div></div>\r | |
398 | <div class="paragraph"><p>is evaluated by SML/NJ on Windows, the result is <span class="monospaced">true</span>. MLton, on\r | |
399 | the other hand, correctly follows the Basis Library Specification,\r | |
400 | which states that on Windows, <span class="monospaced">OS.Path.validVolume</span> should return\r | |
401 | <span class="monospaced">false</span> whenever <span class="monospaced">isAbs = true</span> and <span class="monospaced">vol = ""</span>.</p></div>\r | |
402 | <div class="paragraph"><p>This incorrect behavior causes other <span class="monospaced">OS.Path</span> functions to behave\r | |
403 | differently. For example, when the expression</p></div>\r | |
404 | <div class="listingblock">\r | |
405 | <div class="content"><div class="highlight"><pre><span class="n">OS</span><span class="p">.</span><span class="n">Path</span><span class="p">.</span><span class="n">toString</span><span class="w"> </span><span class="p">(</span><span class="n">OS</span><span class="p">.</span><span class="n">Path</span><span class="p">.</span><span class="n">fromString</span><span class="w"> </span><span class="s">"</span><span class="se">\\</span><span class="s">usr</span><span class="se">\\</span><span class="s">local"</span><span class="p">)</span><span class="w"></span>\r | |
406 | </pre></div></div></div>\r | |
407 | <div class="paragraph"><p>is evaluated by SML/NJ on Windows, the result is <span class="monospaced">"\\usr\\local"</span>,\r | |
408 | whereas under MLton on Windows, evaluating this expression (correctly)\r | |
409 | causes an <span class="monospaced">OS.Path.Path</span> exception to be raised.</p></div>\r | |
410 | </li>\r | |
411 | </ul></div>\r | |
412 | </div>\r | |
413 | </div>\r | |
414 | </div>\r | |
415 | <div id="footnotes"><hr></div>\r | |
416 | <div id="footer">\r | |
417 | <div id="footer-text">\r | |
418 | </div>\r | |
419 | <div id="footer-badges">\r | |
420 | </div>\r | |
421 | </div>\r | |
422 | </body>\r | |
423 | </html>\r |